Teams phone only option ?

Yes, it is possible to restrict Teams to only phone calls. To do this, you can create an Office 365 group for the users you want to restrict, and then set the permissions on the group so that only the phone call features are enabled. This will block the remaining features such as texting, meetings, file sharing, joining channels, and any other non-phone call feature for those users. Note that this restriction would only apply to the users in the group, and not to the entire organization. https://learn.microsoft.com/en-us/microsoftteams/manage-teams-with-policies